I had a leak in my coolant system and it seemed to be coming from the gasket behind the water pump housing. To make a long story short, I replaced the suspicious gasket and the water pump (and its gasket) after taking the housing off.

Now I am trying to do a pressure test before I refill the system. I cannot find the pressure I should pump the system up to and I am searching for it. Does anyone know offhand? Even at 5 psi I saw a leak previously, so that pressure may suffice, but I don't want to overpressurize and cause some more damage...

I pumped up the system to 10 psi and observed a hairline leak in the auxiliary reservoir. My question is, is it reasonable for me to drive before fixing it?

I did use RTV blue to coat the region of the hairline (which is along the central ridge that separates the upper and lower halves). I question whether that will seal it, but am letting it cure before I retest it. I have a road trip next week and would really like to take the Merc. My other leaks seem to be resolved at this point (and they were more like at 5 psi and from the gaskets).

I am really glad I bought this radiator pressure tester. Its really helpful to see where I have leaks before filling the radiator system!

I would be very reluctant to exceed the rating on the cap. There are a lot of components in the cooling system that would probably survive just fine for many more years without entering into what seems the danger zone. Heater core and cylinder head gaskets come to mind. The cap should open at it's rating. Why exceed the normal presure looking for a leak?